1. Field of the Invention
The present disclosure relates to an array substrate for an organic electroluminescent device, and more particularly, to an array substrate for an organic electroluminescent device and a method of fabricating the same.
2. Discussion of the Related Art
Until recently, display devices have typically used cathode-ray tubes (CRTs). Presently, many efforts and studies are being made to develop various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission displays, and organic electroluminescent device (OELDs), as a substitute for CRTs. Of these flat panel displays, OELDs have many advantages, such as high contrast ratio, low power supply, thin profile, wide viewing angle, light weight, stability at a low temperature, simple fabrication, and easy design and fabrication of driving circuit.
The OELD includes an array substrate including thin film transistors that control operations of turning on/off pixel regions.
The thin film transistor of the array substrate includes a semiconductor layer made of polysilicon that has property of high mobility.
The array substrate including the polysilicon thin film transistor is fabricated with about 9 or 10 mask processes.
In other words, 9 mask processes are performed for the array substrate before forming an organic light emitting layer. The 9 mask processes typically comprise: forming a semiconductor layer; forming a first storage electrode; forming a gate electrode; forming an inter-layered insulating film including a semiconductor contact hole; forming source and drain electrodes; forming first and second passivation layers; forming an anode; forming a bank; and forming a spacer.
The mask process is a photolithography process that includes many steps: forming a material layer, on a substrate, that is patterned later, forming a photoresist layer thereon, light-exposing the photoresist layer using a mask including a transmissive portion and a blocking portion, developing the light-exposed photoresist layer to form a photoresist pattern, etching the material layer using the photoresist pattern, stripping the photoresist pattern and the like.
Accordingly, one mask process needs apparatuses and materials for the above respective steps and multiplied by the respective steps.
Accordingly, efforts are made to reduce the mask processes for the array substrate in order to reduce production costs and improve production efficiency.
In addition, the array substrate is designed to include a storage capacitor having a large capacity for image display stability. An overlap configuration is employed to increase the storage capacity per unit area.
However, an area of a pixel region decreases according to a recent trend in display art toward high resolution. Accordingly, even though a storage capacitor is realized through double overlaps, a storage capacity is insufficient for stable image display.
Increase of an area of a storage capacitor to secure a storage capacity causes reduction of an aperture ratio.